Circular cavity slot antenna



Jan. 6, 1959 P. L. KERLEY CIRCULAR CAVITY SLOT ANTENNA U F. ll'vvl/liIll,

Filed Nov. 13, 1956 OSCILLATOR FIG. 2

TRANSMISSION LINE OSCILLATOR INVENTOR, PAUL L. KERLEY.

ATTORNE X in airborne equipment.

United States Patent 2,867,803 CIRCULAR CAVITY SLOT ANTENNA Paul L.Kerley, Albuquerque, N. Mex., assignor, by mesne assignments, to theUnited States of America as represented by the United States AtomicEnergy Commission Application November 13, 1956, Serial No. 621,972

5 Claims. (Cl. 343-769) The present invention relates to antennas andmore specifically to a type of antenna known as a slot antenna which hasincorporated therein a resonant cavity.

The increase in the utilization of radio Waves in aircraft for thepurposes of communication, direction and distance determination and thelike has ca'used a corresponding increase in the number andtypes ofantennas carried by modern aircraft. The reduction of the number ofantennas by utilization of one to perform more than one function and thesuitable design of antennas to 'frequency control for the transmittingoscillator, thus eliminating the need for an anode tuned impedance ortank circuit as a distinct element. In this connection a cavityresonator can be used adjacent to the slot as an additional or alternatetuning device.

An object of the invention is to provide an antenna of small sizeandwith a field pattern suitable for use Another object of the inventionis to provide a novel antenna having a doughnut shaped field pattern andwhich can act both as an antenna and a resonant circuit. The exactnature of this invention as well as other objects and advantages thereofwill be readily apparent from consideration of the followingspecification relating to the annexed drawing in which:

Figure 1 shows one embodiment of the invention with an adjustable centerelement.

Figure 2 shows an embodiment of the invention adapted to transmit over atransmission-line.

Referring now to the drawings, wherein like reference charactersdesignate like or corresponding parts, there is shown in Figure 1 oneembodiment of the antenna excited by an oscillator 18, as shown. Energyfrom oscillator 18 is supplied by means of a suitable transmission line19 to a cylindrical cavity 20 which is shown in longitudinal section asbounded by ABCDEFGH, which includes inner and outer cylindrical walls 17and 21, respectively and lower'and upper walls 23 and 24 respectively.The lower wall contains suitable opening and insulating means as at 25to allow the transmission line to enter the cavity. It is understood, ofcourse, that any other desired entrance means may be used.

The upper wall contains a circular slot 11 which extends into the cavity20 by means of cylinders 13 and 14 as shown. The transmission line isconnected to cylinders 13 and 14 at 26 and 27. In operation, cylindricalcavity 20 will resonate at a particular frequency when suitably excitedby oscillator 18 and circular slot 11 allows radiation of theelectro-magnetic wave in a direction outward from ground plane 10 in adoughnutshaped field pattern, the exact shape of which is determined bythe shape of center element 12.

The loading of the antenna is controlled 'by moving center element 12 inand out perpendicularly to ground plane 10. Conicalcenter element 12 andelements 15 and 16 are contiguous and mechanically rigid so, thatmovement of e1ement12 will occasion relative sliding motion betweensurfaces 16'and 17.

The antenna may be utilized as either an additional or an alternatetuning device for the oscillator. When it serves as the primary tuningdevice or resonant tank circuit of the oscillator, the areas ofcylinders 13 and 14 are made proportional to the desired capacity of thetank circuit and the length of path ABCDEFGH is made proportional to theinductance. The transmission line 19 will then be connected from 26 to27 to the other elements of. the oscillator directly. This manner ofconnection does not form a part of this invention but is given as oneillustration of possible use.

The embodiment in Figure 2 shows another use of the antenna. As can 'beseen from this figure, the center element 12 and elements 15 and 16 havebeen eliminated and the antenna is made concentric with, but nottouching, a single wire transmission line. In all other respects.

the structureof Fig. 2 is'identical with that of Fig. 1. In this way theradio frequency signal can be propagated down a line carrying-anothercurrent, for example. A specific application could be in power linetelemetering systems, where one wire carries both sixty-cycle power anda high-frequency signaling circuit.

It may be noted that the antenna will not work efficiently without somesort of a center conductor, such as the. center elementll of Figure l orthe transmission line of Figure 2. This is due to the fact that theradiated signal has a radial electric field which tends to cancel itselfunless the center conductor is present to act as a shield betweendiametrically opposite portions of the It is thus seen that the antennadisclosed having incorporated therein a resonant cavity has a suitablefield pattern and can be fabricated in a size suitable for airborneapplications.

Obviously many modifications present invention are possible in light ofthe above teachings.- It is therefore to be understood, that within thescope of the appended claims, the invention may be practiced other-wisethan as specifically described.

What is claimed is:

l. A cavity slot antenna comprising first and second conducting coaxialcylinders, two conducting plates, said cylinders being joined at one endby one of said conducting plates, the other plate having a circular slottherein forming inner and outer portions, said slot being concentricwith said cylinders, the other ends'of said cylinders being joinedrespectively to said inner and outer portions conducting flangesextending from said slot toward but not touching said one of the plates,and a cylindrical conductor placed coaxially within said cylinders andextending outwardly from said plates.

2. A cavity slot antenna comprising first and second conducting coaxialcylinders, the space between said cylinders being bounded on two ends byconducting plates, the plate on one end being formed with a circularslot therein, said slot being concentric with said cylinders, flangesextending from said slot toward the plate on the other end, and aconductor placed coaxially within said and variations of the asevgsosfirstand second cylinders and extending outwardly past said conductingplates.

3. A conducting circular cavity slot antenna comprising a. cylindricalresonant cavity bounded by: a first cylinder, a second cylinder coaxialwith and smaller in cross-sectional area than the first cylinder, atfirst plate normal to the first and second cylinders and joining one endof each of said cylinders, a second plate parallel to the first plateand extending inwardly from the other end of the first cylinder, atthird plate parallel to the first plate and coplanar with the secondplate extending outwardly from the other end of the second cylinder, andtwo concentric cylinders each extending from the second and third platespartly toward the first plate; said two concentric cylinders togetherdefining a slot in communication with the cylindrical resonant cavity onone end of the slot, and a cylindrical conductor coaxially placed withinsaid second cylinder and extending outward past thefirst, second, andthird plates.

4. A conducting circular cavity slot antenna comprising a firstcylinder, at second cylinder coaxially within the first, a plateconnecting said first and second cylinders at one end thereof, anoutwardly projecting flange on the other end of the second cylinder, aninwardly projecting flange on the other end of the first cylinder, saidinwardly and outwardly projecting flanges being coplanar but and secondcylindrical walls, a cylindrical slot contained. within said walls, saidslot being formed by flanges ex- 4 spaced from each other, a end to theinwardly projecting flange coaxially within the first cylinder andprojecting toward but not touching the connecting plate, a fourthcylinder attached at one end to the outwardly projecting flange andcoaxially within the third cylinder and projecting toward but nottouching the connecting plate, and a conductor placed coaxially withinthe second cylinder and extending outward past the projecting flanges.

5. A coupler for coupling high frequency currents from an oscillator toa transmission line comprising a cylindrical resonant cavity coaxialwith and surrounding a. transmission line, said cylindrical cavityhaving first tending from one end of said walls inwardly from the outerwall and outwardly from the inner all and then' coaxially with thetransmission line and said walls, and

an oscillator connected to said resonant cavity at the flange-formedslot, whereby electromagnetic radiation radiated through said slot willcoact with andbe transmitted by said transmission line.

References Cited in the file of this patent UNITED STATES PATENTS2,834,959 Dorne May 13, 1958 third cylinder attached atone I

